The association of renal disease and pulmonary hypoplasia (Potter's Syndrome) in the newborn infant is well known but the pathogenesis of the disorder remains unknown. Comparative biochemical studies suggest that arginase may have an important function outside of its common association with the urea cycle. Kidney arginase may be of importance in an arginase - ornithine - proline pathway where imino acids are required for special protein synthesis. The chick embryo contains high kidney arginase but no liver arginase. Preliminary studies indicate that early embryonic nephrotoxic renal injury results in hypoplastic lungs in the fetus or newly hatched chick. This change is believed due to a reduction in kidney function with diminished arginase activity which results in a deficiency of proline and amino acids essential for mesenchyme maturation. This defect may produce an abnormal mesenchyme epithelial interrelationship required for normal lung development. This concept is to be pursued using a specially designed electrolytic radiorespirometer for in vivo physiologic and biochemical studies to be correlated with in vitro biochemistry and histopathology.